TDengine TSDB

Global – October 28, 2026 -- QoS 1 is the practical starting point for most industrial telemetry over MQTT, but none of the three QoS levels guarantees a complete historian, according to engineering guidance tied to the OASIS MQTT 5.0 standard.

QoS 1 reduces the risk of losing a message on an MQTT delivery hop. The receiving system must tolerate duplicates. QoS 0 fits replaceable readings where low overhead matters more than complete delivery. QoS 2 is reserved for flows where duplicate delivery on that hop is unacceptable and the extra protocol exchange is justified.

MQTT QoS covers one sender-receiver hop, not the whole pipeline

The OASIS MQTT 5.0 standard defines QoS for a single delivery flow. A device publishing to a broker is one flow. The broker sending to a subscribing collector is another, and it can use a different QoS depending on the original publication and the subscriber's granted maximum.

Global – October 28, 2026 -- Neither MQTT retained messages nor persistent sessions can guarantee complete production history, so industrial operators who need every measurement must add application-level buffering and a historian, according to an engineering analysis of the OASIS MQTT 5.0 specification.

Retained messages deliver the latest state to new subscribers

A retained message gives a subscriber the last retained value on a topic when it subscribes. In the example of a packaging line publishing to plant/line2/packer/status, a new maintenance display receives the retained RUNNING state without waiting for the next live publication, provided the message is still available and the subscription's retain-handling settings permit delivery.

Global – October 27, 2026 -- Industrial teams can locate missing historian records by tracing one test message across five boundaries: broker receipt, subscriber receipt, parsing, database write and query. The approach comes from troubleshooting guidance on TDengine's MQTT ingestion, which warns that a live broker feed or a connected publisher proves only part of the chain.

One tagged test message anchors the diagnosis

Engineers should publish a single message for one equipment tag through the approved production path, such as plant/line2/pump07/pressure. They should log the exact topic, payload bytes, broker timestamp, publisher identity, destination table and intended source timestamp. Each test needs a fresh timestamp, because identical timestamps can make a successful write indistinguishable from an earlier one.

Global – October 27, 2026 -- Even QoS 2's exactly-once delivery covers only one MQTT sender-receiver flow, not the subscriber's database transaction, so an MQTT broker cannot serve as an industrial historian. A broker moves messages between publishers and subscribers. A historian keeps time-indexed records that engineers can query, trend and aggregate later.

Broker retention mechanisms fall short of historical storage

A retained message is only the current message for a topic, and a new one normally replaces the prior state. A persistent session preserves subscriptions and eligible queued messages for an offline client. Session expiry, broker capacity, message expiry and administrative policy can all limit what remains.

Broker persistence protects broker state across restarts. It does not define table schemas, engineering timestamps, multi-year retention, SQL queries, aggregates or audit-ready change history.